Using Subdomains in Version 2.1.7

I've followed the procedure of installing subdomains according to https://django-subdomains.readthedocs.io/en/latest/ but when I try

python3 manage.py runserver

I get the error

from django.core.urlresolvers import reverse as simple_reverse
ModuleNotFoundError: No module named 'django.core.urlresolvers'

What would be the problem?

django-admin version => 2.1.7
OS platform => Kali Linux

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